Apparatus for testing color



June 23, 1942. o. E. NELSON APPARATUS FOR TESTING COLOR Filed Dec. 14, 1939 INVENTOR Qscne E/VZSO/V. /2W

A TORNEY V Patented June 23, 1942 2,287,322 7 APPARATUS FOR. TESTING coma PATENT Os'car E. Nelson, Tyrone, Pa., assignor to West Virginia Pulp and. Paper Company, New York,

N. Y., a corporation of Delaware Application December 14, 1939, Serial No. 309,142

1 Claim- (Cl. 250- -41.5)

My present invention relates to an improved apparatus for testing color, and more especially for testing the reflecting qualities of surfaces, as for example, paper. Among the objects of my invention is to provide means for imparting to the current of the photoelectric cell a substantially true sine characteristic, so that when the current is amplified the output of the amplifier will be substantially proportional to the input.

Other objects and advantages thereof will be apparent from the following detailed description taken with the annexed drawing in which:

Fig. l is an isometric view of a preferred embodiment with the cover removed; while Figures 2, 3 and 4 show the characteristics of the current produced in the photoelectric-cell, depending upon the relation of the size of window of the cell to that of the vanes producing an interruption of the light beam;

Figs. 2 3 and 4 show diagrammatically the relationship of vane to window opening re-' sponsible for the current characteristics as illustrated in Figs. 2, 3 and 4, respectively.

Referring to Fig. 1, ill-denotes alight source formed preferably of a light bulb of a type consuming approximately 7.5 amperes at l volts, such current being supplied by the aid of a voltage regulator l2 disposed in a 1l0volt circuit of alternating current, as shown, and a transformer H, the devices mentioned being standardin the art for the purposes specified. The light from bulb l0 passes through a condenser [3, an infra red heat filter l4, and then through any one of the various filters Ilia, Nib, Hie, etc., desirably arranged on a wheel l6 whereby any desired filter may be brought into operative position. Preferably each filter element l6a,-etc. is provided with an iris diaphragm l5, each-of which is adjustable as by a screw device l5a. Each of the filter elements [6a, etc. passes a definite band of wave lengths, which bands collectively will'cover the visual spectral range, i. e., from 400 to'100 millimicrons wavelength. Preferably the filter elements are arranged in a definite order according to the wave length ascribed to each. By virtueof this form of device, light of one wave length may be readily substituted for another over a desired range by rotating the wheel to bring the desired light-filter into the path of the light beam. Alternatively a prism maybe used the position of which can be varied slightly to furnish light of the desired comparatively narrow frequency range. Y The light passing froma filter element I6 is directed upon a surface I'I which is either a standard of comparison such as a block of- I magnesium carbonate or the specimento be 1 tested. The element His supported upona plate Hi having an aperture l8a of suitable size not substantially larger than the cone of light passing to and from the reflecting surface in order .to eliminate stray rays of light. The. angle of the incident beam to the surface of element ll susceptible of variation, but I have found an a rotary shutter I9 comprised of spaced vanes 19a, the-spaces |9b between the vanes beingv of. f

substantially the same size as the vanes themselves. The shutter I9 is attached to a'spindle and-spindle *being enclosed in .a housing lflj, which in turn is resiliently secured to thebottom ofthe cabinet by means of screws 199. speed of the motor may be controlled through rheostat l9h. The interrupted light beam now is caused to fall upon the window of photoelectric cell 20 by the aidgof condensing lens 2| above which isheat filter 22, the elements 20, 2l,'22-being disposed in a cell 23 having an aperture 24 of a size-having a relation to the vanes [9a. such'that the shadow v ,30 of the vane is closel y equal to'the size of the aperture 24, thereby producing a fluctuating cur I rent in, the photoelectric cellhaving a substan- I tially true sine characteristic such as shown-in A Fig. 2. Fig. 3 illustrates the situation where the 5' shadow vof vane 19a. is less than the area of the aperture 24, thereby producing a sincewave which is less than 100% modulated and of less" j amplitude than that of Fig. 2'. Fig.- 4 shows the situation where the vane shadowis larger than the aperture, producing in excess of 100% modulation' and a distorted sine wave.

vThe output from cell 20 is fed to of known type 25 comprising a seriesof thermigalvanometer 26. x

-' 'In the use of the R. P. M., thereby interrupting the light 24,200

55 times per minute for the shutter shown having I 'FFica angle of around 47' degrees to give the best re- I sults. The beam reflected from the element I1 is preferably periodically interrupted by means of The an amplifier onic tubes the output from which'. is '-fe d to-a" device astandard of comparison, as for example a magnesium carbonate block, is placed behind the'a rtur lm, aparticular filter element of thewheel I selected,

50 as forexample that in the lowest rangejof the I spectrum, the light Ill lighted, -and-.the'shutt er, J u

; l9 setin rotation by means of-motorflllldwhich drives the. shutter at suitable speed;le.=-'g.,. .2200.

eleven vanes and producing a pulsating current capable of being amplified by the amplifier 25. The iris diaphragm I! of the filter selected is now adjusted so that the indicator or galvanometer 26 reads an arbitrary value, say 98, corresponding to the reflecting power of the magnesium carbonate surface of substantially 98%. The wheel I6 is turned so as to bring into operative position a new filter element, which may be either the next one in the spectral series or such other one as it is desired to use in the test, whereupon the iris diaphragm l associated with that filter element is adjusted as previously described to give the reading on the galvanometer of 98. The process of calibration described is then repeated for as many filter elements as may be involved in the test. The magnesium carbonate block is then removed from over the aperture la and replaced by the surface to be tested, as for example, a sheet of paper. when this ha been done a series of readings of the galvanometer are then taken, one each for the filter elements-involved in the test, without, however, altering the setting of the iris diaphragms which have been previously determined. From the foregoing it will be evident that the galvanometer readings will give an accurate measure of the reflecting power of the sample tested for the particular wave bands used. It is possible to use a single iris diaphragm which would be mounted in the path of the beam of light and independently of the wheel I 6. This arrangement, however, requires that the diaphragm be calibrated by means of the magnesium carbonate block each time a different filter element is used.

Since in each case the intensity of the light from the standard of comparison is regulated so as to give the samereading, i. e., of 98, on the indicator, the amount of light energy received by the photoelectric cell is always the same foreach wave band when using the standard of comparison. It will therefore be apparent that once it is determined that intensities up to this maximum lie upon the straight line portion of the output curve of the photoelectric cell, the

amplified in other ways, as for example, by using' an uninterrupted light beam and producing a steady current in the photoelectric cell which is used to bias the receiving grid of a themionic amplifier.

'While I have illustrated and described in detail certain preferred forms of my invention, it is ,to be understood that other changes may be made therein and the invention embodied in other structures. I do not, therefore, desire to limit myself to the specific construction illustrated, but intend to cover my invention broadly in whatever form its principle may be utilized.

I claim:

In a device for measuring the reflection characteristics of a surface to be tested, and employing a photoelectric cell against which a beam of light from said surface is impinged, a thermionic amplifier for said cell and an indicating device actuated thereby, the improvement which consists in the combination with the foregoing of a light interrupting device in the path of said beam to said cell, said device consisting of a plurality of movable vanes and means for driving same, an apertured diaphragm coacting therewith whereby to periodically interrupt said light beam, said vanes and the aperture being so arranged that the shadows of said vanes cast upon said aperture are substantially equal in size and area to said aperture whereby a current of substantially modulation and of substantially sine form is produced in said cell and of a frequency facilitating the amplification of said current by said amplifier.

OSCAR E. NELSON. 

